Reflector microwave antenna systems are widely used in radar and in microwave communications to concentrate the energy emitted from a transmitter or incoming to a receiver. A major field of use is in satellite communications systems both to transmit signals to the satellite and from the satellite and for earth stations which receive the signals from the satellite broadcasts.
Two mirror systems are widely known and are interesting because they move the focus of the energy from a point in front of the primary reflector, usually a paraboloid, to a point at, or near, the center of the primary reflector. The form of the systems used parallel the telescope systems referred to as Gregorian and Cassegrain where the main difference is related to the form of the curve on the secondary reflector.
The advantages that accrue to the use of these systems is that they eliminate the need for a support for a preamplifier unit at the primary focus and lead in transmission lines and place the incoming signal at a convenient position to directly attach the receiver amplifiers and other apparatus near the rear of the main reflector. In addition the secondary reflectors can be of such a design as to minimize the effects of diffraction induced signal "spill". The resulting effect is to make the antenna relatively more efficient than the simple paraboloid reflector and much more convenient to use and service.
There are two main drawbacks to the current designs. One is that the support used for the secondary reflector must be in the path of the microwave energy and may either distort the signal or attenuate it significantly leading to loss of signal quality. The other substantial disadvantage to the prior art devices is that they are quite massive units for the diameter of the primary reflector and the additional structure used to support the secondary reflector adds still further to the weight. The mass of the system restricts the locations where the unit can be installed. It also adds to the complexity and drive requirements and the mountings needed for supporting and aiming the unit.
One of the major uses for these antennas is in earth stations for receiving direct broadcast signals from satellites. For this application it would be desirable to have lightweight units capable of being mounted on rooftops in order to be used in small buildings as well as larger ones. None of the prior art antennas seem capable of being reduced sufficiently in weight to accomplish this without substantial performance penalties.